1. Field of the Invention
The present invention relates to an inline electron gun and a color cathode ray tube using the same. More specifically, the present invention relates to a cylindrical electrode and a flat plate electrode with holes, which make up a main electrostatic lens of the inline electron gun.
2. Related Background Art
In conventional inline electron guns, as disclosed in JP 4(1992)-133247 A, for example, a main electrostatic lens is made up of a G3 electrode and a G4 electrode. The G3 electrode includes: a cylindrical outer electrode with a common aperture having an approximately oval-shape in cross-section and surrounding three electron beams; and a flat plate electrode provided within the outer electrode and having three passage holes for letting each of three electron beams pass therethrough. The G4 electrode has the same configuration as the G3 electrode.
In the following, the G3 electrode and G4 electrode included in the conventional inline electron gun disclosed in the above publication will be explained, with reference to FIG. 4. FIG. 4A is a cross-sectional view of the G3 electrode and G4 electrode in the conventional inline electron gun, FIG. 4B is a front view of the G3 electrode from the arrow A of FIG. 4A, and FIG. 4C is an enlarged view of a part of the flat plate electrode illustrated in FIG. 4B.
In FIG. 4A, reference numeral 41 denotes a cylindrical electrode with an aperture having an approximately oval-shape in cross-section, 42 also denotes a cylindrical electrode with an aperture having an approximately oval-shape in cross-section, 43 denotes a flat plate electrode provided within the cylindrical electrode 41, and 44 also denotes a flat plate electrode provided within the cylindrical electrode 42. These cylindrical electrode 41 and flat plate electrode 43 make up a G3 electrode 410, and the cylindrical electrode 42 and the flat plate electrode 44 make up a G4 electrode 420. Reference numerals 45 to 47 denote passage holes provided in the flat plate electrode 43, and 50 to 52 denote passage holes provided in the flat plate electrode 44. These passage holes are provided for letting three electron beams pass therethrough.
The three passage holes provided in each of the flat plate electrodes, as shown in FIG. 4B, are arranged along the inline direction (hereinafter also referred to as a xe2x80x9chorizontal directionxe2x80x9d). FIG. 4B shows the passage holes 45, 46 and 47 provided in the flat plate electrode 43. The opening geometry of the passage hole 46 and that of the passage hole 47 are symmetric with respect to a center line of the passage hole 45 along a direction orthogonal to the inline direction (hereinafter referred to as a xe2x80x9cvertical directionxe2x80x9d). It should be noted that the geometries of the passage holes 50, 51 and 52 provided in the flat plate electrode 44 have the same as the passage holes 44, 45 and 46, respectively.
As shown in FIG. 4C, the passage hole 45 located at the center of the three holes provided in the flat plate electrode 43 has an oval shape with a major axis along the vertical direction. Whereas, as shown in FIG. 4C, the passage hole 47 located at either outer side (FIG. 4C shows the passage hole 47 only) has an outer half portion 49 in a semicircle shape and an inner half portion 48 configured in a higher-order curved shape with a degree of n more than 2 and not more than 3. It should be noted that in this specification the xe2x80x9cinner sidexe2x80x9d refers to a direction toward the passage hole located at the center of the flat plate electrode, while the xe2x80x9couter sidexe2x80x9d refers to a direction away from the passage hole located at the center of the flat plate electrode.
In this way, the G3 electrode 410 and the G4 electrode 420 that make up a main electrostatic lens of an inline electron gun include: the outer cylindrical electrodes 41 and 42 with an opening geometry in an approximately oval shape with a major axis along the horizontal direction as shown in FIG. 4; and the flat plate electrodes 43 and 44 provided within the cylindrical electrodes 41 and 42, respectively, arranged at a recessed position from each opening of the cylindrical electrodes, and having three passage holes.
With this configuration, electron beams passing through the center passage holes 45 and 50 are acted upon by an independent electric field formed by the passage holes 45 and 50 and a superimposed electric field formed by the straight-line portion of the periphery of the cylindrical electrodes 41 and 42. Electron beams passing through the passage holes 46 and 51 or 47 and 52, located at both outer sides, are acted upon by an independent electric field formed by the passage holes 46 and 51 or an independent electric field formed by the passage holes 47 and 52, and the superimposed electric field formed by the curved-line portion of the periphery of the cylindrical electrodes 41 and 42.
In the conventional inline electron guns, a convergence function (static convergence) for three electron beams can be optimized by appropriately selecting the degree n of the higher-order curved portion (e.g., 48 in FIG. 4C) of the passage holes 46, 47 and 51, 52 at either outer side of the flat plate electrodes 43 and 44, facing to the central passage holes 45 and 50, and therefore an electron beam that reaches a screen finally can be made close to a perfect circle.
Now, in order to change the size of a cathode ray tube so as to be increased or decreased in size, and not redesigning the above-described conventional inline electron gun, then the cathode ray tube increases or decreases in size along the tube axis direction, which would degrade the static convergence property of three electron beams on the screen.
In the case of a small change in the size of the cathode ray tube, such degradation in the static convergence property may be improved with a magnet or the like disposed outside of the cathode ray tube.
However, when the static convergence property deteriorates beyond the capability of such a magnet or the like, a design of components of the electron gun and the applied voltage have to be changed so as to give a higher priority to the static convergence property on the screen.
More specifically, in order to maintain the static convergence property, the opening geometry of the passage holes provided in the flat plate electrodes of the G3 electrode and the G4 electrode has to be changed significantly, or the voltage applied to the G3 electrode has to be changed. As for the change in the voltage applied to the G3 electrode, there are many restrictions such as the voltage to be applied becoming so high that dielectric breakdown might occur, or the applied voltage cannot be changed in terms of the power source. In such cases, a pitch of small apertures in a G1 electrode has to be changed.
In addition, such a substantial change in the passage holes in the flat plate electrodes of the G3 electrode and the G4 electrode and the aperture pitch of the G1 electrode would lead to a situation where an assembly jig of the electron gun used before change cannot be used, and therefore a new assembly jig should be prepared, which would increase the cost of the assembly of the electron gun.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an inline electron gun and a color cathode ray tube including the same, by which the manufacturing cost for an assembly jig of the electron gun can be reduced, for example, that might be generated with a change in the size of the cathode ray tube, and a favorable static convergence property can be realized.
To fulfill the above-stated object, an inline electron gun according to the present invention emits three electron beams aligned along a horizontal direction, and the inline electron gun includes: a cylindrical low potential side electrode provided with a first flat plate electrode; and a cylindrical high potential side electrode provided with a second flat plate electrode, where the low potential side electrode and the high potential side electrode are arranged in the stated order along a direction in which the electron beams are headed so as to make up a main electrostatic lens. In the inline electron gun, each of the first flat plate electrode and the second flat plate electrode has a central passage hole for letting a central electron beam of the three electron beams pass therethrough and two outer passage holes for letting each of the other two outer electron beams pass therethrough. Each of the opening geometries of the two outer passage holes in the first flat plate electrode and each of the opening geometries of the two outer passage holes in the second flat plate electrode are configured with a higher-order curve. Each of the opening geometries of the two outer passage holes in at least one of the first flat plate electrode and the second flat plate electrode is formed by combining two higher-order curves having different degrees with a boundary on a center line of the outer passage hole along a vertical direction. An opening geometry of one outer passage hole and an opening geometry of the other outer passage hole provided in a same flat plate electrode are symmetric with respect to a center line of a central passage hole provided in the same flat plate electrode along the vertical direction, and in a higher-order curve forming the opening geometries of the outer passage holes provided in the first flat plate electrode, at least one of (a) inner portions of the higher-order curve located at the side of the central passage hole with respect to the center lines of the respective outer passage holes along the vertical direction and (b) outer portions of the higher-order curve located outside have a different degree from that of corresponding portions of a higher-order curve forming the opening geometries of the outer passage holes provided in the second flat plate electrode.
To fulfill the above-stated object, a color cathode ray tube according to the present invention includes at least the above-described inline electron gun according to the present invention.